UK police have opened an investigation into claims of a Westminster pedophile ring, saying they have a list of about 40 alleged child abusers, including over 10 current and former British politicians.

Whistleblower Peter McKelvie, whose claims prompted Operation Fernbridge, disclosed in his the latest report that up to 40 members of parliament and peers knew about or took part in the child abuse network.

Operation Fernbridge is a Scotland Yard investigation into allegations of a pedophile network with links to Downing Street.

Lawmakers - including former ministers and household names - from all three main political parties are included on the list.

Some of the alleged child abusers remain active in the UK parliament, while several others, including Cyril Smith and Peter Morrison, have already died.

"I believe there are sufficient grounds to carry out a formal investigation into allegations of up to 20 MPs and Lords over the last three to four decades, some still alive and some dead. The list is there," McKelvie said.

At least one witness has told police that he was abused by a Tory MP when he was under 10 years old in the 1980s.

Prime Minister David Cameron has ordered Mark Sedwill, the permanent secretary for the UK's Home Office, to conduct an internal investigation into what happened to the dossier.

Other cases of child sexual abuse have been reported in the country.

Several high-profile figures have been arrested in connection with the multiple investigations into the abuse scandal surrounding Jimmy Savile, a disgraced former TV host with the state-funded British Broadcasting Corporation (BBC). He died in 2011, but, following his death, hundreds of allegations of sex abuse and rape of minors became public.